In oil wells, it is common for sand or other solid gritty materials to be carried from the producing formation along with the oil into the wellbore. Sand or other grit causes problems and wear for the production equipment and preventing the introduction of such solids into the wellbore is very much desired. A common solution to prevent the production of such sand and grit is called “gravel-packing” the well. Gravel packing is basically the installation or packing of coarse sand or gravel material into the annular space between the production tubing/liner and the casing or the formation in an open-hole production arrangement. This gravel packed space extends along the outside of the production tubing/liner, may be the length of hundreds of pipe sections or joints. While most of the production tubing is impervious to liquid, the sections or joints adjacent the production zone are provided with slots or other pre-perforated openings in the peripheral wall. These joints allow the produced liquids to pass from the outside of the production tubing into the interior of the production tubing. These slotted or pre-perforated joints are often screened and/or pre-packed with sand control media and known to those skilled in the art as sand control screens. The interior of the production tubing is where a pump may be disposed to carry or drive the liquids to the surface. Those that are skilled in the art understand that there are a lot of different production methods including free flowing and plunger lift as well as several variations of artificial lift such as gas lift, rod pumps, rotary PC pumps, jet pumps, electric submersible pumps and there are other less common methods of production methods.
The slotted or pre-perforated joints are commonly referred to as base pipe and typically includes holes or openings with a wire mesh, screen, or pre-packed sand control media around the outside to prevent the sand or gravel from leaking into the production tubing. There are other gravel packing arrangements where the base pipe has many small slits that are sized to prevent the passage of sand, but the function is substantially the same. Gravel packing essentially forms a filter barrier for the fine formation sand or grit, but allow the liquids to pass freely through the interstices into the production tubing and be carried to the surface. However, the sand or gravel does not discriminate between different fluids and there are times when undesirable fluids enter the gravel packing. For example, as a well is produced, water, especially salt water, often encroaches into the hydrocarbon production zone as hydrocarbons are extracted. Typically, hydrocarbons and water are found together underground with water below oil. As the hydrocarbons are withdrawn, the hydrocarbon/water interface rises and it is not uncommon for water to begin to comprise a significant portion of the total fluids produced. However, water can enter virtually anywhere in the completion in the well depending on the geological conditions. Water may enter the mid to upper sections of a producing zone when the upper sections have higher permeability and when the permeability ratios (vertical vs. horizontal) or natural formation fractures favor a situation where water may over-run the tighter producing zones and show up first in mid to upper areas of the completion.
While the hydrocarbon/water interface may initially be confined to a single production zone, it is also not uncommon for an oil well to be drilled such that several oil bearing zones are accessed by the single well. Each of the hydrocarbon bearing zones may be isolated from one another by impermeable rock formations and each may have and hydrocarbon/water interface. The gravel packing may be exposed to several of these formations and fluids from one may translate along the gravel packing media to enter the production tubing at a different location. This can be a concern as allowing different isolated zones to communicate with one another may create undesirable problems in that one zone may contaminate another. The separate zones may extend for miles so cross contamination may have broad consequences.
There have been several efforts to stop the production of water in gravel packed wells. Typically, the formation pressure that drives the hydrocarbons toward the low pressure well comes from salt water that is denser than hydrocarbons and, therefore, below the hydrocarbons. As such, the efforts have been focused on closing the gravel packed bed from the water at the bottom of the production zone. What hasn't been developed is a suitable and effective technique to seal the well from undesirable fluids that are above or in the middle of the target zone while permitting continues production from the target zone.